This invention generally relates to methods of assembling plastic structures, and in particular to a method of welding plastic parts to form various types of electrochemical cells made from such parts, such as electrolyzers.
Electrolyzers are electrochemical devices that serve to separate fluids into constituent parts, typically water into hydrogen and oxygen. In certain electrolyzers, the fluid, which may include water and other electrolytes, are circulated though one or more cells to which an electric current or charge is applied. The constituent hydrogen and oxygen are collected at or near electrode surfaces and eventually are forced to flow out in an effluent stream for storage or use. The throughput of such electrolyzers may vary greatly, but increasingly high throughput is desired for efficient production of industrial quantities of gas.
Certain electrolyzer arrangements have been proposed that use synthetic plastic materials for internal cells in which water is broken into hydrogen and oxygen. Such plastics are a common material used for many structures, as they provide important benefits, such as low-weight, chemical resistance, electrical insulation, and ease of processing. Assemblies made from multiple or complex plastic parts have been available for many years. However, as the complexity of the plastic parts increases, the need for techniques for joining complex plastic parts has increased. Challenges in the effective joining of such plastics are particularly acute for demanding structures such as the internal components of electrolyzers.
Many techniques have been used to join plastic parts together to form larger structures. In many applications, the thermoplastic parts are thermally welded to form assemblies. Welding is a relatively low-cost technique that provides a strong and often hermetically-sealed joint. However, welding generally requires access to the surfaces of the parts that are to be joined to form the structure. When a structure has a complex internal geometry, welding may not sufficiently join the internal structures of the parts. Other welding techniques, including ultrasonic welding, laser welding, induction welding, friction welding and the like, may also require access to the surfaces to be welded.
As welding may not be practical for complex assemblies, plastic parts may be joined by adhesives. However, adhesives often have some disadvantages over welding. For example, the extra materials used for adhesive bonding may add to the overall cost of an assembly. Further, adhesives may not be as strong as the plastics themselves, leading to potential failures at the seam between the parts. Further, adhesives may have a hardening period, or setting time, which adds to the cycle time for producing structures. Finally, any adhesives used must be resistant to the materials contacting the structure, such as alkaline electrolytes.
Complex plastic parts may also be joined by solvent welding. In solvent welding, an appropriate solvent is used to soften the plastic surface, prior to placing the surface in contact with the surface of another part. However, while the solvent used may be lower cost than adhesives, solvent welding shares many of the same disadvantages, including the time required for the solvent to evaporate or diffuse from the plastic and allow the parts to bond and harden.
Accordingly, there is a need for techniques to join complex plastic parts that have complex internal structures, such as electrolyzers.